Important requirements for materials used in boiling water nuclear reactor construction include low absorption for thermal neutrons, corrosion and stress--corrosion resistance and mechanical strength. Zirconium-base alloys sufficiently satisfy these requirements that they are widely used for such purposes, "Zircaloy-2" (containing about 1.5 per cent tin, 0.15 per cent iron, 0.1 percent chromium, 0.05 per cent nickel and 0.1 per cent oxygen) and "Zircaloy-4" (containing substantially no nickel and about 0.2 per cent iron but otherwise similar to Zircaloy-2) being two of the important commercial alloys commonly finding such use. These alloys, however, are not nearly all that one would desire, particularly in respect to accelerated pustular corrosion which occurs under boiling water reactor normal operating conditions and results in spalling of thick oxides from channels and thickening of oxides on fuel rods. The spalling of oxide flakes leads in some instances to development of high radiation fields in the vicinity of control rod mechanisms where the flakes collect; and the presence of thick oxide layers reduces heat transfer efficiency and can result in local overheating of fuel cladding.
Reports in the prior art of efforts to solve this generally recognized problem do not reveal any real success Thus, in U.S. Pat. No. 3,005,706, it is proposed that from 0.03 to 1.0 per cent of beryllium be added to zirconium alloys intended for use in conventional boilers, boiling water reactors and similar apparatus to enhance corrosion resistance to high-temperature water. Similarly, in U.S. Pat. Nos. 3,261,682 and 3,150,972, cerium and/or yttrium and calcium, respectively, are proposed as zirconium alloy additions in like proportions for the same purpose. Accounts of the long-term results of such compositional changes are sparse, however, and commercial zirconium alloys do not include these additional constituents.